Prions, Darwin's Friend

blamanj writes "Prions, the recently discovered bits of protein thought to be responsible for mad cow disease are turning up all over. It has been shown that prions change the behavior of yeasts, and may therefore offer a speedy way for yeast to evolve."

Comments

Re:Mad Yeast Disease?

[Anonymous Coward]

The same prions that are suspected to be the cause of Mad Cow Disease. See the connection? Yeah, the parent is definitely on-topic.

Except that these prions are not at all related to the Mad cow disease ones. "Prion" is a class of infectious substance, akin to "bacterium" or "virus". It's a relatively new class, so the mad cow disease ones are best known, but saying "Yeast prions will give you vCJD" is like saying "plant bacteria will give you tuberculosis".

mechanism for variable expression in vertabrates?

[oliphaunt]

from the article:

In its non-infectious form, the protein normally helps to read and convert the DNA code into other proteins. But in its infectious form, the prion stops working. This means that many proteins are manufactured slightly sloppily.

The team believes that prions may therefore offer a speedy way for yeast to evolve, because those cells with the infectious prion churn out a whole range of slightly altered proteins. Normally this is bad news for the yeast, but when the cells find themselves in a tough spot, one or two of them may grow better in the new conditions as a result, and so help the colony to survive.

This is interesting for a number of reasons, but the one that sticks out in my mind is the transfer of plasmids between prokaryotes. Eukaryotes, like eyu and me, don't pass our DNA around as casually as, say, Staphlococcus Aureus does. This has the benefit that our DNA is relatively stable, meaning that we are almost guaranteed to be able to breed with someone two or three generations younger than we are ourselves (hellOOOO, Hef!) but the trade-off is that we're not very responsive to environmental stressors that require quick adaptation to survive.

In simpler terms, through conjugation live bacteria can pick up spare DNA from other living bacteria and immediately "evolve" to meet a new environmental challenge without needing to wait for another generation to be born before the mutation can take effect. The plasmid DNA is then passed along to the daughter cells of successuful bacteria. This obviously confers huge selective advantages on bacteria which pick up plasmids that code for antibiotic resistance genes.

I interpret this prion research in yeast to suggest that yeast can experience the same kind of variable protein expression as bacteria, throught the mechanism of prion inactivation. This is significant because eukaryotic cells do not experience conjugation, and generally do not have plasmids, but DO transport various small proteins across the cell wall and into the cytoplasm.

And if it works for yeast, perhaps the prion mechanism is intended to perform the same function in humans, or in the cows that end up with BSE. The test would be to find some gene in a higher mammal that expresses one way when a prion is in conformation A, but expresses another way in conformation B...